Haemophilus

1. Haemophilus This is a group of small; Gram negative, pleomorphiccocco-bacilli that required enriched media usually containing blood or its derivatives

2. Haemophilusinfluenzae • H. influenzae is found on the mucous membrane of the upper respiratory tract in humans. It is an important cause of meningitis, acute epiglottitis and septic arthritis in infant and young children and occasionally causes respiratory tract infections in children and adults. • Morphology: Small Gram negative cocco-bacilli .pleomorphic. • Organisms in young cultures have a definite capsule used for typing H. influenzae.

3. Culture Characters: • Facultative anaerobes grow on blood agar, and better chocolate agar, each provided with the two growth factors that require for H. influenzae respiration namely factor X and factor V. • Factor X(haemin); is required for the synthesis of the respiratory enzyme cytochrome C. • Factor V (nicotinamide adenine dinucleotide ,NAD); is essential for oxidation-reduction processes in cell metabolism.

4. H. influenzae is non hemolytic. • Around staphylococcal colonies the colonies of H. influenzae grow much larger this phenomenon is called 'satellite phenomenon' this is because staphylococci produce factor V. • Biochemical reactions Oxidase positive, catalase positive, reduce nitrate to nitrite, ferment glucose some types indole positive or urease positive.

5. Antigenic structure: Encapsulated H. influenzae contains capsular polysaccharides, used for its typing. Of the six serotypes (a-f) Type b causes most of the severe invasive diseases such as meningitis and sepsis.

6. Pathogenesis & virulence factors H. influenzae infects only man there is no animal reservoir. • It is important as a pathogen of infants and young children meningitis, acute epiglottitis and septic arthritis), although it can causes diseases to individuals of all age groups. • It enters the body through the upper respiratory tract (by inhalation) resulting in either asymptomatic colonization or infections such as otitis media sinusitis, acute epiglottitis, bronchitis or pneumonia.

7. The organism produces IgA protease that degrades secretoryIgA, thus facilitates attachment to the respiratory mucosa. • After establishment in the upper respiratory tract the organism may enter the blood stream and spread to meninges or joints. • Meningitis is mainly caused by the encapsulated H. influenzae type b 'Hib' strain.

8. The antiphagocytic capsule and the endotoxin participate in pathogenesis of disease production. Most infections occur in children between the age of 6 months and 6 years. • Other infections causes by H. influenzae are; cellulites - bacteremia & osteomyelitis.

9. Laboratory diagnosis: • Specimens; pus, sputum, blood or CSF. • Direct examination; Gram stain immuno-fluorescence or the specimen 1s mixed directly with specific antisera (type b) for capsule swelling reaction. • Immunologic detection of type b polysaccharide antigen in body fluids or pus using latex agglutination test.

10. Culture: • On chocolate agar enriched with factor V and factor X. H. influenza grow around X and V factor only. Treatment: • The mortality rate of untreated H influenzae meningitis may be up to 90%. The drug of choise for meningitis or other serious systematic infections caused by H. influenzae is ceftriaxone & related cephalosporins followed by chloramphenicol, ampicillin and trimethoprimsulfamethoxazole.

11. Prevention: • Haemophilus b conjugate vaccine the vaccine contains the capsular polysaccharide of H influenzae type b, conjugated to diphtheria toxoid. It is given some time between the age of 2 and 15 months. • This vaccine is much more effective in young children than the unconjugated vaccine. • Meningitis, in close contacts to the patient can he prevented by rifampin.

12. Haemophilusaegyptius(Koch weeks bacilli) • It resembles H. influenzae closely, require X & V factor for growth. • H. aegyptius associated with a highly communicable form of acute purulent conjunctivitis (pink eye), also it is the etiological agent of Brazilian purpuric fever ; a disease of children characterized by fever, purpura, shock and death. Treatment : • Tetracycline topically.

13. Haemophilusducreyi • It resembles H. influenzae closely but require X factor only for growth. • It is the etiological agent of a sexually transmitted disease called chancroid, (soft chancre). Chancroid is ulcer on the genital with marked tenderness and swelling - The regional (bubo). • lymph nodes are enlarged and painful.

14. Treatment: • The drug of choice is erythromycin followed by ciprofloxacin, then ceftriaxone.

15. Haemophilusaphrophilus • It resembles H influenzae closely but requires X factor in primary isolation only and excess CO2. • The organism is a normal flora of the oral and respiratory tract. It is sometimes encountered in infective endocarditis or pneumonia.

16. Haemophilusparainfluenae • It is resembles H. influenzae closely, but requires V. factor. It is a normal flora of respiratory tract. • It may cause subacuteendocarclitis, conjunctivitis andurithritis.

17. Haemophilushaemolyticus • It is resembles H. influenzae closely, requires X & V factors But it is hemolytic organism, it form beta haemolysis on blood agar. • It is one of the normal flora in the nasopharynx. • It may cause urinary tract infections in childhood or rarely upper respiratory tract infections.

18. Gardnerella(Haemophilus) vaginalis • It s resembles H. influenzae closely, but not required X & V factors. • It is normal inhabitants of female genitor-urinary tract. • It may cause non specific vaginitis characterized by a foul smelling discharge. • Vaginal discharge shows epithelial cells (clue cells) with tiny gram negative coccobacilli (suggest non specific vaginitis).

19. Treatment • metronidazole.